A Mg2 ion - Ca2 ion - activated actomyosin-like ATPase has been isolated from bovine, cat and rat brain. It can be dissociated into actin-like and myosin-like components on Sephadex G-200 columns or by ultracentrifugation in a continuous sucrose gradient. These are concentrated in the synaptosomal fraction. The broad objectives of this project are to study further the chemistry, distribution, changes with development and aging, immunological properties and function of these proteins in brain. Emphasis will be focused on the proteins isolated from the synaptosomal fraction. The syaptosomal fraction will be further subdivided into vesicular and membraneous fractions and the distribution of the protein will be determined. Whether or not a tropomyosin-like system functions in the control of the enzymatic activity of the proteins will be investigated. Amino acid composition will be studied by enzymatic digestion procedures. The turnover rate of the protein will be studied by radioisotope labelling procedures as will binding of the labeled proteins to synaptic membranes and vesicles. Localization of the actin will be studied by interaction with muscle heavy meromyosin and of brain myosin by immunologic techniques. Whether the myosin-like moiety can be split into heavy and light fractions will also be investigated.